This invention relates to a reproduction characteristics control device for an audio device reproducing various sound fields by producing reflected sounds of a reproduced source signal and, more particularly, to a control device of this type capable of correcting a frequency-response characteristic easily to a standard frequency response characteristic or other predetermined frequency response characteristic in accordance with an actual reproduction environment, e.g., a space inside an automobile or a listening room. The invention relates further to a reproduction characteristics control device of the above described type having an improved impression of presence.
In the field of audio devices, attempts have been made to reproduce various sound fields in a selected reproduction environment, e.g., a space inside an automobile or a listening room. These attempts aim at reproducing tones in a selected reproduction environment with an atmosphere as if one was present in a real sound field such as a concert hall.
In the prior art sound field reproduction, reflected sound characteristic parameters of various reproduced sound fields are prestored in a memory such as a ROM, these reflected sound parameters are read out by a user's operation for designating a reproduced sound field and operated with a reproduced source signal to produce a reflected sound signal, and this reflected sound signal is propagated from sound field reproducing loudspeakers disposed at four corners of the reproduction environment.
An attempt has recently been made to apply the above sound field reproduction technique to an audio device mounted on an autombile so as to reproduce a desired sound field in an automobile. A frequency response characteristic in a space inside an automobile, however, is a peculiar one which is different from one in a listening room in that frequency response is generally high in a low frequency region and low in a high frequency region. The frequency response inside an automobile varies also greatly with the type of the automobile (i.e., passenger car, commerical car, station wagon etc.), size of the space inside the automobile, the number of passengers, the listener's position, characteristics and location of loudspeakers and other factors.
For obtaining a sufficient sound field reproduction effect, therefore, it is necessary in the prior art device to manipulate a graphic equalizer or the like device to correct the frequency response characteristic to a standard characteristic (i.e., a flat characteristic). This correction, however, requires an extremely troublesome operation for users.
In some sound fields to be reproduced, the sound reproduction effect can be enhanced by correcting the frequency response characteristic to a predetermined characteristic (e.g., a characteristic in which a certain frequency band is emphasized). In this case also, correction by users involves a troublesome operation.
It is, therefore, an object of the invention to provide a reproduction characteristics control device for an audio device capable of correcting a frequency characteristic easily in accordance with a reproduction environment or with a reproduction environment and a sound field to be reproduction and thereby effectively realizing reproduction of a desired sound field.
There is another problem in conventional audio devices mounted on an automobiles. In the conventional audio devices mounted on automobiles, loudspeakers are generally disposed at rear left and rear right positions in an automobile. A listener, however, cannot have a sufficient impression of presence from such loudspeaker arrangement. Besides, such loudspeaker arrangement has the disadvantage that power tends to concentrate on rear parts only.
For overcoming these probelms, various types of four channel devices have been proposed.
FIG. 12 shows an example of such prior art four channel devices. The device of FIG. 12 is one in which source signals of left and right channels are simply distributed to front loudspeakers and rear loudspeakers. In this device, source signals of left and right channels reproduced by a playback device (including, e.g., a cassette tape recorder, a tuner and a Compact Disc player) are distributed to front channels and rear channels respectively and propagated from loudspeakers 158-161 disposed at front left, front right, rear left and rear right positions in a space 156 inside of an automobile through power amplifiers 151-154.
FIG. 13 shows another example of the prior art four channel devices in which a reverberation component contained in a source signal is emphasized to produce an impression of presence in a simulating manner. In this device, source signals of left and right channels reproduced by a playback device 162 are inverted in their phase by phase inverters 164 and 166 and these phase-inverted signals and source signals which are opposite phase to each other are added to each other to produce an L-R signal and R-L signal (i.e., the reverberation component in the input source signals). These L-R and R-L signals are suitably emphasized by amplifiers 172 and 174 and are added to the source signals by adders 176 and 178. Among the sum signals, signals for front channels are propagated from loudspeakers 158 and 159 disposed at front left and front right positions in a space 156 of an automobile. The sum signals for rear channels are delayed by delay circuits 184 and 186 to produce a feeling of presence in a simulating manner and thereafter are propagated from loudspeakers 160 and 161 disposed at rear left and rear right positions in the space 156 through amplifiers 182 and 183.
FIG. 14 shows also a prior art device which produces an impression of presence by emphasizing a reverberation component contained in a source signal. For front channel sounds, source signals of left and right channels reproduced by a playback device 190 are propagated by loudspeakers 158 and 159 disposed at front left and front right positions in a space 156 of an automobile. For rear channel sounds, a right channel source signal is inverted in phase by a phase inverter 192 and added to a left channel source signal by an adder 194 to produce an L-R signal. This L-R signal is emphasized suitably by an amplifier 198, delayed by a delay circuit 202 and thereafter is propagated by a rear left loudspeaker 160 through a power amplifier 204. The L-R signal is also inverted in phase by a phase inversion circuit 206 to produce an R-L signal. This R-L signal is amplified suitably by an amplifier 208 and added to the right channel source signal by an adder 210. The sum signal is delayed by a delay circuit 212 and thereafter is propagated by a rear right loudspeaker 161 through a power amplifier 214.
The device of FIG. 12 which simply distributes source signals cannot reproduce a desired sound field and, moreover, reproduction of source sounds tends to become somewhat unnatural.
The devices of FIGS. 13 and 14 which produce presence in a simulating manner simply emphasize a reverberation component contained in a source signal and fail to reproduce a selected sound field from among various sound fields such as a concert hall, a church, a stadium etc.
It is, therefore, another object of the invention to provide a reproduction characteristics control device capable of reproducing a desired sound field in a space inside of an automobile.